1. Field of the Invention
The invention relates to a dual clutch for a heavy-duty powertrain with two torque input shafts and pre-selected transmission clutch engagements for multiple-ratio transmission gearing.
2. Background Art
Heavy-duty powertrains for trucks and other heavy-duty vehicles, both road vehicles and off-road vehicles, typically use a multiple-ratio synchronized transmission with a neutral clutch situated between torque input elements of the transmission and a vehicle engine, such as a high-torque, spark-ignition engine or a compression ignition Diesel engine. It is known design practice to use a transmission with a torque input gear that driveably engages one or more lay shafts, the torque input gear being coaxially disposed with respect to a torque output shaft. In powertrains of this type, multiple-range gearing may be used on the torque output side of the transmission to establish two or more torque ratio ranges. Power is delivered to vehicle traction wheels through a differential-and-axle assembly. Mechanical synchronizer clutch mechanisms may be mounted on each lay shaft, as well as on the common axis of the torque input gear and the torque output shaft.
The neutral clutch used with manually-controlled transmissions of this type must be opened and closed in sequence with actuation of the synchronizer clutch mechanisms during torque ratio changes. Release of the neutral clutch will result in interruption of torque delivery during a ratio shift event as synchronizer clutches establish and disestablish torque flow paths to a transmission main shaft, which in turn can be driveably connected to the transmission torque output shaft. In contrast, certain automated manual transmission systems may establish torque interruption to facilitate engagement and disengagement of the synchronizer clutches by defueling the engine during a ratio shift to momentarily interrupt engine torque delivery to the transmission torque input shaft. In the case of a spark-ignition, internal combustion engine, torque interruption can be effected also by momentarily retarding spark timing.
It is known design practice also to use a dual neutral clutch with dual friction disks in heavy-duty powertrains. The friction disks are engageable in tandem to establish a high torque capacity torque flow path and to interrupt torque delivery from the engine to a torque input shaft for the transmission during a gear ratio change event. Use of dual friction disks in a dual clutch reduces wear rate of the friction disks since the friction torque delivery burden is shared by two disks rather than a single friction disk. The operating diameter of each friction disk, furthermore, can be reduced, which improves the packaging efficiency of the powertrain in the vehicle.